Traditionally, people leave handwritten notes for family members, friends, co-workers, and others in “can't miss” places to ensure that their messages are received. For example, paper messages may be pinned on bulletin boards, post-it notes may be attached to computers or chairs, notes may be left on counters, etc. As people's lives become increasingly busy, however, it can be challenging to communicate constant changes in plans and schedules, as the traditional handwritten note is not very effective for communicating promptly with others. Some of the shortcomings associated with physical messages may be overcome by the use of electronic messages. Electronic messages have the advantage of being quickly delivered to a user. Determining how to send a message to users, however, is becoming an increasingly challenging problem. Each user to whom a message is addressed may have several electronic devices, including a mobile phone, one or more computers, a personal digital assistant (PDA), and other devices. In addition, each user may have access to various electronic services via their electronic devices, including voice and text messaging, email, instant messaging, and other services. With so many devices and communication services, it can be difficult to coordinate communication with family members, friends, co-workers, and others. The need therefore exists for a system that overcomes the above limitations, in addition to providing other benefits.